Embodiments of the present disclosure generally relate to a liquid panel assembly, and more particularly, to a liquid panel assembly configured for use with an energy exchanger.
Enclosed structures, such as occupied buildings, factories and the like, generally include a heating/ventilation/air conditioning (HVAC) system for conditioning outdoor ventilated and/or recirculated air. The HVAC system includes a supply air flow path and an exhaust air flow path. The supply air flow path receives pre-conditioned air, for example outside air or outside air mixed with re-circulated air, and channels and distributes the pre-conditioned air into the enclosed structure. The pre-conditioned air is conditioned by the HVAC system to provide a desired temperature and humidity of supply air discharged into the enclosed structure. The exhaust air flow path discharges air back to the environment outside the structure. Without energy recovery, conditioning the supply air typically requires a significant amount of auxiliary energy, particularly in environments having extreme outside air conditions that are much different than the required supply air temperature and humidity. Accordingly, energy exchange or recovery systems are used to recover energy from the exhaust air flow path. Energy recovered from air in the exhaust flow path is utilized to reduce the energy required to condition the supply air.
Conventional energy exchange systems may utilize energy recovery devices (for example, energy wheels and permeable plate exchangers) or heat exchange devices (for example, heat wheels, plate exchangers, heat-pipe exchangers and run-around heat exchangers) positioned in both the supply air flow path and the return air flow path. Liquid-to-air membrane energy exchangers (LAMEEs) may be fluidly coupled so that a desiccant liquid flows between the LAMEEs in a run-around loop, similar to run-around heat exchangers that typically use aqueous glycol as a coupling fluid.
In general, a LAMEE transfers heat and moisture between a liquid desiccant solution and air through a thin flexible membrane. A flat plate LAMEE includes a series of alternating liquid desiccant and air channels separated by the membrane. Typically, the pressure of the liquid within a liquid channel between membranes is higher than that of the air pressure outside of the membranes. As such, the flexible membranes tend to outwardly bow or bulge into the air channel(s).
In order to avoid excessive restriction of the air flow due to membrane bulge, air channels of a LAMEE are relatively wide compared to the liquid channels. Moreover, a support structure is generally provided between membranes to limit the amount of membrane bulge. However, the relatively wide air channels and support structures typically diminish the performance of the LAMEE. In short, resistance to heat and moisture transfer in the air channel is relatively high due to the large air channel width, and the support structure may block a significant amount of membrane transfer area. Accordingly, a large amount of membrane area is needed to meet performance objectives, which adds costs and results in a larger LAMEE. Moreover, the support structure within an air channel may produce an excessive pressure drop, which also adversely affects operating performance and efficiency of the LAMEE.
Typically, desiccant flows through a solution panel, which may include membranes that contain the desiccant between air channels. In general, the solution panel is uniformly full of desiccant during operation. Known energy exchangers force flow of desiccant upwardly through the solution panel, against the force of gravity. As such, the desiccant is typically pumped from the bottom of the solution panel to the top with enough pressure to overcome the relatively large amount of static head pressure, as well as the friction in the panel. However, the pumping pressure causes the membranes of the solution panel to outwardly bow or bulge. Moreover, the pumping pressure is often great enough to cause leaks in the membranes. Further, the pressure of the desiccant being pumped through the solution panel often causes membrane creep and degradation over time.
A typical solution panel also includes a filler material, such as a wick or woven plastic screen, configured to ensure proper spacing between membrane surfaces within the solution panel. The flow of the desiccant through the filler material is generally uncontrolled. For example, the filler material is generally unable to direct the desiccant over a particular path. Instead, the flow of desiccant through the filler material follows the path of least resistance, which generally follows a Hele-Shaw pattern between closed-spaced plates. Further, the flow pattern of the desiccant is sensitive to variations in the spacing within the solution panel caused by even small amounts of membrane bulge. Also, fluid instabilities from concentration and temperature gradients may cause additional flow irregularities and mal-distributions. The winding flow pattern within a typical solution panel produces flow dead zones at or proximate corners of the solution panel.
As noted, in order to ensure that desiccant completely fills the solution panel from bottom to top, a relatively high pumping pressure is used. However, the pumping pressure may often generate membrane bulge and bowing, which may adversely affect the energy exchanger.